Chisago County Goes After Gullies

A rock dam controls and slows water, reducing its power to erode and carry soil and other material. (Photo Chisago Soil & Water Conservation District)

Stabilizing the St. Croix watershed, one gully at a time. (Photo Chisago Soil & Water Conservation District)

The bluffs of the St. Croix Valley stand crumbling over the river, millennia of weather worrying away sandstone and limestone which settled out of seawater half a billion years ago.

In the span of a few football fields, the land drops a hundred, maybe two hundred feet, down to the floodplain. Sheer cliffs jut above steep slopes formed by everything that falls off the soft rock, and covered with soil and trees.

The hills are threaded with game trails, speckled with bright but reclusive birds and flowers, picketed by white pines that are a memory of the river two centuries ago, all of it beautiful and beloved. From the top, there are vast vistas.

Thing is, the topography doesn’t always make it easy to keep the St. Croix clean. When farm fields, lawns, and other human surfaces flush rainfall, the water can cut far more and far deeper gullies than normal.

“When rainwater goes through gullies, it sends tons of soil and plant matter into the river,” says Deb Ryun of the St. Croix River Association. “That stuff muddies the waters and fuels the growth of harmful algae.”

A little runoff can be responsible for big impacts downstream: If a pound of phosphorus runs into the river, it can translate to 300-500 lbs. of harmful algae growth.

But it’s possible for the bluffs to crumble at their natural pace again, for phosphorus and soil to be landlocked. Gullies are fixable.

There are two major ways to neutralize a problem gully: slowing the water going down the bluff, and holding the soil in place to prevent further erosion.

Reducing the flow usually means building berms and a depression at the top of a bluff to capture runoff during rainstorms. As the water is slowly released, the sediment and phosphorus settle to the bottom. Holding the soil in place is done with rocks, vegetation, netting, and manual labor.

“Thanks to Clean Water Funding, we have been able to identify and tackle a major erosion issue along the St. Croix River, and the end result is having a direct impact on the downstream water quality,” says Craig Mell, the district administrator.

Chisago started targeting gullies in 2011. They began by figuring out where the most damaging gullies were located along the St. Croix, from near Scandia north to Wild River State Park. The team investigated almost 500 gullies, and identified 36 that were actively eroding and a serious problem for the St. Croix. Those three dozen became their top priorities.

They also got started working on two urgent projects where large amounts of soil were eroding and into the river. Both of the sites had been of concern to the agency and private landowners for years.

“Because of the size and associated cost to correct the problems, these projects have never been completed,” the agency reported.

With the Legacy Amendment funding, the projects were finally finished.

The Chisago Soil & Water Conservation District has been doing gully work ever since, with impressive results, thanks to continued funding from the Legacy Amendment and the Minnesota Board of Water and Soil Resources.

By 2014, more than 10 projects had been completed. Last year alone, 15 sites were stabilized.

At the city of Taylors Falls’ Public Works facility, they targeted a 1,600-foot-long gully that emptied right into the St. Croix. By building a basin to capture and slowly releasing rainwater over the 24 hours after a storm, 32 tons of sediment and 32 lbs of phosphorus are expected to be kept out of the river each year.

In another project, on private property near the river, simple water control structures will capture 75 lbs of phosphorus on its way to the St. Croix.

At 400 pounds of harmful algae per pound of phosphorus, that one project could potentially prevent 15 tons of algae from growing in Lake St. Croix.

The work has continued this summer, like a well-oiled gully-stopping machine.

Not only are more gullies being stabilized, Chisago is also taking what they’ve learned to the Sunrise River, which joins the St. Croix at the upstream edge of Wild River State Park. The Sunrise is the fifth-biggest source of phosphorus that pollutes Lake St. Croix.

The bluffs bordering the St. Croix River are often admired, standing tall and wide over their wooded valley. But the water flowing below them is more fragile than any sandstone. By healing the bluffs, Chisago is defending the river.